Acoustic Flow Monitor Records Small Debris Surges on the South Fork...

On September 28, 2013, after about 10 hours of steady rain, an acoustic flow monitor (AFM) on the South Fork Toutle River recorded the passage of a small debris flow. The AFM showed significantly elevated signals for about three hours as water, mud and rock rolled downstream in short surges. Crews visited the area to see the evidence -- remnant debris flow surfaces on channel margins, new deposits, mud lines and bent, scoured alders. The flow likely traveled for over a mile downstream of the AFM location. No damage to infrastructure was reported.